Beam power tube



Jan. l1, 1949.

D. G. HAINES BEAM POWER TUBE Filed Jan, 8. 1946 /QTTO/P/VE Y PatentedJan. 11, 1949 BEAM POWER TUBE Donald G. Haines, Elmhurst, Ill., assignorto National Union Radio Cor poration, Newark, N. J.,

a corporation of Delaware v Application January 8, 1946, Serial No.639,848 3 Claims.4 (Cl. 25u-27.5)

This invention relates to electron discharge devices, and moreparticularly to electron tubes of the so-called beam power type.

A principal object of the invention is to provide a beam power tubehaving a plurality of separate emitting cathodes with a specialconstruction of beam forming electrode for improving the operatingcharacteristics of the tube.

Another object is to provide a duplex cathode beam power tube having animproved beam forming electrode construction which acts to confine withgreater uniformity the secondary electron beams from the plate or outputelectrode.

A feature of the invention relates to a novel beam forming electrode forelectron tubes of the screen grid type whereby the screen grid potentialis rendered substantially independent of secondary emission from theplate.

Another feature relates to a beam power tube having a series of parallellinearly extending cathodes with a common control grid, a common shieldgrid, and a common beam forming electrode, the beam forming electrodebeing constructed so that the l-ow or zero potential zone between thescreen grid and plate is maintained uniform without substantiallyaffecting the mutual conductance of the tube.

A still further feature relates to the novel organization, arrangement,.and relative location of parts which provide an improved beam type tubecapable of handling relatively large power outputs with a, minimum ofdistortion,

Fig. 1 is a schematic plan View of a tube embodying the invention.

Fig. 2 is a vertical sectional view of a tube according to Fig. 1.

Fig. 3 is a modification of Fig. 1.

Referring to Fig, 1, there is shown in schematic form an evacuated andenclosing envelope I, within which are mounted two elongated electronemitting cathodes 2, 3, each preferably in the form of a flattened metalsleeve whose external peripheral surface is coated with electronemissive material. These cathodes when in use are raised to electronemitting temperature by any well-known heating means (not shown).Preferably the cathode sleeves have opposite flat and substantiallyparallel faces 4, 5, and 6, 1. Surrounding both cathodes is a commonforaminous control grid 8 which may be in the form of a ne wirelhelically wound around the usual metal uprights or side rods 9, I0, towhich the individual grid turns are fastened. These individual gridturns are usually referred to as grid laterals. Likewise surrounding thecathodes, is

e a common screen grid I I, which may be of a construction similar tothe grid 8 and having side rods I2, I3. Preferably, and as is usual inbeam power tubes, the grid laterals of screen grid I I are aligned withthe corresponding grid laterals of control grid 8 so as to form theelectrons from the respective cathodes into a series of parallel layersextending towards the common plate or outputA anode I4. Anode I4 may besupported on suitable metal uprights l5 and I6.

In order to` achieve `the desired beam characteristics', preferably thegrids 8 and Il should be in the form of flattenedA helices so that thegrid rlaterals lie in respective planes which are substantially parallelto the at faces of the cathodes. In order that the tube may have thedesired mutual conductance characteristics, it is important that thespace between the screen grid II and the'plate or anode I4 be as freefrom obstruction as possible. At the same time, in order to control anyundesired secondary electron emission from the surface of the plate I4,it is important that a uniformly low or even zero potential zone beestablished at the appropriate location between the screen grid and theplate. This is particularlytrue where the beams from the cathodes are tobe confined to certain restricted areas ofA the plate. Accordingly,there is provided a beam confining or forming electrode systemcomprising two sections I 'I, I8, each of which is suitably supported onits respective metal upright or side rods I9, 20. These beam formingelectrodes may be of any suitable crosssectional shape, and each hasfins 2 I-22, 23-24, extending partially into the space between screengrid II and plate I4 so as to provide the necessary 10W potential Zoneat the desired region therebetween. i

With the construction as described, the side rods 9, II), I2, I3, aremounted in a common plane so that there is an electron shadow in thevicinity of these siderods. However, when the beam plates I1, I8, areconnected to ground cr some other suitable low base potential, theyprovide a shield against the return of secondary electrons from theplate to the screen grid I I or to the control grid 8. At the same time,these beam plates act to conne the desired electron beams from thecathodes to the desired restricted areas of the plate I4.V In otherwords, by suitable shaping of the beam plates, the primary electronbeams are shaped as indicated by the dotted outlines in Fig. 1, and atthe same time the space lying outside the boundaries of` these connedbeams are protectedagainst returning secondary 3 electrons to the shieldgrid or control grid. However, since two separate cathodes are employed,it is not entirely feasible to make sure that the respective beamstherefrom overlap suciently to protect the entire active space betweenthe screen grid and the plate against returning secondary electrons.Thisunprotected spacesis indicated schematicallyrin the drawing bythedotdash outline. In accordance with the invention, there are providedadditional rods or metal strips 25, 26, which extend parallel to thelength of the cathodes and each of these strips or rodsis .preferablylocated in substantially the same vrplane as the corresponding fins2l-22, 223-224, .and are electrically connected thereto by suitablemetal strips or the like. With this arrangement, it is possiblethereioreftohave eachfcathode produce its individual coniined beam whichis acted upon in common by the respective common grids 8 and Il, andthese individual beams reach the plate t4 without any substantialVoverlap. `Howeverjthegpresence of the'inembers'25 VandZ- introduces inthe unprotected space above- Vmentioned-a suitable Apotential `so thatthere is provided a `substantiallyuniform zone extending transversely tothe electron beams, whichzone is of suiciently lowpotential gradienttofprevent return of substantially Aall secondary electrons from; theplate Id lto anysection of the grid ll or the grid 8. It will beunderstood of coursethat whenthe tube is in use, Athe screen-grid Il' isoperated at a suiciently high positive potential with respect to theycathode so that this high "potential does not have any eiect beyond theplane defined by the ns 2l-22 and 23-24.

With the Yforegoing described' arrangement the control of the primaryelectron'beams emanating from the respective cathodes is materiallyincreased, and results in higher `plate impedance and a higheramplification factor. One possible explanation for this is that theeffectiveplate `area or zones 27, 28, 29, 3S, on whichA the'primaryelectrons impinge are not aiected by the presence of the additional rodsor-strips 25, 26. lConsequently, these rods or strips may be made 'sothin, considered transversely to the electron beam, that the mutualconductance of the tubeis not appreciably `reduced thereby. On the otherhand ythe relatively high positive potential of the plate .26.Therefore, `the plate impedance-of the'tube is increased since the'distance from "each 'cathode o.; 'to the equivalent triode plate isincreased, land Athe,.amplification factor is increased because theequivalent triode is also further removed-from the control grid'Referring to Fig. 2, there is shown in vertical 60 sectional view atypical construction of electrode mount embodying the principlesexplained in connection with Fig. 1. The parts of Fig. 2 whichcorrespond structurally and functionally to those of Fig. 1 aredesignated by the `same. numerals. n Fig. 2, the electrodes aren'supported Ifrom-a common glass header or base 3l which vis-sealed intothe bottom of the bulb l but `in the usual manner. Sealed through theheader-3i are suitable contact prongs and lead-in members'32-39 llto`which:areiastened as `by-.welding the respec- Vnected by a short metalstrap'to the lead-in 34,

'which may also be connectedrto"therbeam'forming electrode system. Asshown in Fig. 2, the beam forming electrode system is in the form of arectangular metal box having rectangular windows in its sides facing theflat surfaces of the 5 cathodes, these Windows being sufficiently largeso that the side ns 2l-22, 23-2l5, extend inwardly .towards thelongitudinal axis of the "mount, a .distance slightly beyond the ends ofthe screen grid Il. The horizontal upper mar- .lo gins 40 and thecorresponding horizontal lower `margins 4I of each window thereforeconstitute :inzeiect braces between the two beam forming sections l'land I8. This type of beam forming platemay therefore be readily stampedout of a mffsingle Ysheet of strip metal and the necessary rigidity andfixed dimensions of the windows are thereby assured. '.The members 25and 25 above described might then be readily welded at their oppositeends to the horizontal straps 40 and 4I of each window, and thesemembers 25 and '25 in `accordance 'with the inventionV are locatedmid-waybetweenthe cathodes 2 ari-d3.

While there has been* described a duplex lcath- `ode beam power tube, itwill 'be understood that 35 'the-invention' isnot limited to suchA atube,'com

"prising `only 'two separate cathodes and a corresponding 'singlexpairof members v25, 25. As shown in Fig. Sythe same'principle may beembodied in a larger 'output tube by employing more than ntwo separatecathodes. Thus, as shown 1n this figure, the' tube'has a series of fourelectron-emitting .cathodes 42, 43, 44, $5, and located .mid-way'between 'each adjacent pair of cathodes are'located a correspondingpair of space 3;,.shie'1dingro'ds or strips'46-ll, ll8-9f50-5l,corresponding to .the members .25 and 26 of Fig. l. "In thisembodiment-fthe remaining parts of the electrode .system Y whichcorrespond` structuruall'yland.functionally to those of Fig. l and.2,bear 4U .the same. designation numerals.

`While certain particular embodiments have been described herein,various changes and modi- ,cations-.maybe made therein, withoutdeparting i :fromtthe spiritaandrscope'of the invention. l V`What isclaimed is:

l. An amplifier tubeof the beam power type Uconfiprfising "a pair ofsubstantially parallel and :spaced-Y linearY cathodes; a control Vgrid.surroundo =ing said cathodesa shield .grid Asurrounding'isaid4controlwgridganv output anode for said `cathodes, a pair ofbeam=formingfelements mounted {adjacent `.the end sections Yoisaidgrids, and a conductive member mounted inr said. region and con--inectedto zsaidaelements to 'provide a fl'etarding potential gradientin said region with'i'espectto electrons tending .to movefrom the anodevtoward fthe control fgrid, said "beam-forming elements cooperating withsaid cathodes to'forin the elec- Y`tron .streams tinto respective randsubstantially :non-.overlappingiibeams diverging towards said anode:andwith a .region between said beams havingy low electron density.

:linnn electron discharge tube of the beam :power '.typecomprising apair of substantially `linearand f parallel Lspaced l cathodes, a`control gr-idsurrounding said cathodes, a shield grid surrounding thecontrol grid, an output anode surrounding-the shi-eid grid, meanssurrounding-the shield -gri'd "and 'having end Aportions which cooperatewith said cathodes to form the electrons finto separater andsubstantially non-overlapping beams, said means having `Loppositelydisposed v`windows facing'the'cat'hodes and each kwindow Lhaving a"transverse 'metal strip electrically -connected thereto and locatedmidway between said cathodes.

3. An amplier tube of the beam power type, comprising, a pairofsubstantially palallelrand spaced linear cathodes, a controlgridsurrounding said cathodes, a shield `grid ,snrxjonnding said controlgrid, an voutput VUanqdesurrounding said shield grid, a box-likelmetalmember having two of its opposite wallsfacing said cathodes and eachprovided with a respective window for the passage of electrons from saidcathodes to said anode, the Walls of said box-like member constituting apair of electron beam-forming' plates, and a narrow metal stripextending acrossv each of said windows parallel to said cathodes andlocated symmetrically with respect to'said cathodes, said beam-formingplates co-aetingY with said cathodes to form the electrons from' saideathodes into respective and substantially non-overlapping beams with aregion between the beams of relatively low electron density wherein saidnarrow metal strips are located, said strips serving to provide aretarding potential gradient in said region with respect to electronstending to move from the anode toward the con- Great Britain Aug. 30,1937

